Rotational speed control system, rotatingly driving system, air blow system, clean bench, outdoor unit of air conditioner

ABSTRACT

This invention relates to a rotational speed control system including a plurality of motor drivers for driving motors, and the object thereof is to drive a plurality of motors at the same rotational speed without depending on the number of motor drivers and without depending on the characteristics of each motor driver. A remote controller  31  and a motor driver  202  are connected to a motor driver  201 . The motor drivers  201  and  202  control motors M 11  and M 12  at a prescribed rotational speed, respectively. A rotational speed instructing signal  91  indicative of the rotational speed is supplied from the remote controller  31  to the motor driver  201 , and further supplied from the motor driver  201  to the motor driver  202 . Because the rotational speed instructing signal  91  indicates a rotational speed which is transmitted in a digital value between the motor drivers  201  and  202 , both of the motors M 11 and M   12  are driven at the rotational speed indicated by the rotational speed instructing signal  91.

TECHNICAL FIELD

This invention relates to a rotational speed control system including aplurality of motor drivers for driving motors. This invention isapplicable to a clean bench and an air blow system blowing air into theclean bench, and an outdoor unit of an air conditioner using the airblow system.

BACKGROUND ART

Conventionally, it has been sometimes required that a plurality ofmotors be rotated at the same rotational speed. FIG. 5 is a blockdiagram showing the configuration of a publicly worked air blow systemthat provides the same quantity of air from a plurality of fans. Becausen fans F₁, F₂, . . . F_(n) are designed in accordance with the samespecifications, motors M₁, M₂, . . . M_(n) for rotating the respectivefans are set to be rotated at the same rotational speed.

The motors M₁, M₂, . . . M_(n) are driven by motor drivers D₁, D₂, . . .D_(n) respectively. The motor drivers D₁, D₂, . . . D_(n) supply drivingvoltages V₁, V₂, . . . V_(n) to the motors M₁, M₂, . . . M_(n)respectively. The rotational speeds T₁, T₂, . . . T_(n) of the motorsM₁, M₂, . . . M_(n) are detected by rotational speed detectors P₁, P₂, .. . P_(n) respectively and sent to the motor drivers D₁, D₂, . . .D_(n).

Motor drivers D_(i) (i=1, 2, . . . , n) each include a resistor R_(0i).In each of the motor drivers D_(i), a voltage across the resistor R_(0i)is input to an operation unit CPU which determines a driving voltageV_(i) based on this voltage and allows a driving circuit DRV to supplythe driving voltage V_(i) to a motor M_(i).

The voltages across the resistors R_(0i) depend on a current I suppliedfrom a remote controller CO and the number n of the motor drivers D_(i).The motor drivers D_(i) are all designed in accordance with the samespecifications, and ideally an equation (1) holds:R ₀₁ =R ₀₂ = . . . =R _(0n) =R ₀  (1)

Accordingly, when the motor drivers D₁, D₂, . . . D_(n) are connected inparallel with respect to the remote controller CO as shown in FIG. 5,based on the assumption that the input impedance of the operation unitCPU is sufficiently high, currents I₁, I₂, . . . , I_(n) flowing throughthe resistors R₀₁, R₀₂, . . . , R_(0n) respectively are equal to eachother, and an equation (2) holds:I ₁ =I ₂ = . . . =I _(n) =I/n  (2)

Because the motor drivers D_(i) are all designed in accordance with thesame specifications, an equation (3) holds for the driving voltages:V ₁ =V ₂ = . . . =V _(n)  (3)

Thus, when the motors M₁, M₂, . . . M_(n) are designed in accordancewith the same specifications, the rotational speeds T₁, T₂, . . . T_(n)are equal to each other, whereby the same quantity of air is providedfrom the n fans F₁, F₂, . . . F_(n).

The rotational speeds T₁, T₂, . . . T_(n) are adjusted by adjusting themagnitude of the current I supplied from the remote controller CO. Forthis reason, the remote controller CO is provided with a variableresistor Rv for current value setting.

As described above, in the conventional technique, the current I issupplied from the remote controller CO and the magnitude of the currentI is adjusted to thereby adjust the same quantity of air provided fromthe n fans F₁, F₂, . . . F_(n). Therefore, the rotational speedfluctuates only slightly even when the distance between the remotecontroller CO and the motor drivers D₁, D₂, . . . D_(n) increases whichleads to a lot of resistance in the wiring length between them. It isalso resistant to extraneous noise.

However, as is evident from the equation (2), a current I_(i) that issupplied to each of the motor drivers D_(i) and generates the voltageacross the resistor R_(0i) depends on the number n of the motor driversD_(i). Therefore, a voltage input to the operation unit CPU in each ofthe motor drivers D_(i) varies when the number n of the motor driversvaries.

On the other hand, because the single remote controller CO is connectedto a plurality of motor drivers, the current I output from itself andthe same quantity of air provided from a plurality of fans are set inone relationship without consideration of the number n. Therefore, inorder to obtain the quantity of air in accordance with the relationshipset at the remote controller CO even when the number n varies, it isnecessary to reset the relationship between the voltage across theresistor R_(0i) and the driving voltage V_(i) at each of the motordrivers D_(i).

Besides, although the equation (1) holds ideally, the values of theresistors R_(0i) sometimes vary among the motor drivers D_(i). In thatcase, the current I_(i) supplied to each of the motor drivers D_(i) alsovaries, which in turn may cause rotational speeds T_(i) to vary. And inthat case, the quantities of air provided from the fans F₁, F₂, . . .F_(n) will vary as well.

DISCLOSURE OF INVENTION

This invention has been made in view of the above circumstances, andprovides a technique for driving a plurality of motors at the samerotational speed without depending on the number of motor drivers andwithout depending on the characteristics of each motor driver.

In a first aspect of this invention, a rotational speed control systemcomprises:

-   -   (a) at least one or more motor drive chains (71; 72) each        comprising: (a-1) rotational speed instructing means (31; 32)        outputting a rotational speed instructing signal (91; 92)        setting a motor rotational speed; (a-2) a first motor driver        (201; 211) receiving the rotational speed instructing signal        from the rotational speed instructing means and driving a motor        (M₁₁; M₂₁) corresponding to itself based on the rotational speed        instructing signal; and (a-3) at least one second motor driver        (202 to 206; 212) capable of communicating with the first motor        driver in a digital value, receiving the rotational speed        instructing signal from the first motor driver and driving a        motor (M₁₂ to M₁₆; M₂₂) corresponding to itself based on the        rotational speed instructing signal, and (b) central monitoring        means (10) monitoring the operations of the first and second        motor drivers in units of the motor drive chains by        communicating with the first motor driver of each of the motor        drive chains.

According to the rotational speed control system of the first aspect ofthis invention, because the rotational speed instructing signal settingthe motor rotational speed is set, supplied to the first motor driver,and also to the second motor driver in a digital value, a plurality ofmotors can be driven at the same rotational speed in units of air blowchains without depending on the number of motor drivers and withoutdepending on the characteristics of each motor driver.

In a second aspect of this invention, in the rotational speed controlsystem according to the first aspect, in each of the motor drive chains(71; 72), (a-4) an in-chain wiring (51; 52) connecting the first motordriver (201; 211) and the second motor driver (202; 212) to each otheris further provided.

According to the rotational speed control system of the second aspect ofthis invention, the rotational speed instructing signal is supplied fromthe first motor driver to the second motor driver via the in-chainwiring.

In a third aspect of this invention, in the rotational speed controlsystem according to the first aspect, the motor drive chains (71; 72)include a plurality of motor drive chains.

According to the rotational speed control system of the third aspectthree of this invention, the motors can be driven at an equal rotationalspeed in units of motor drive chains.

In a fourth aspect of this invention, in the rotational speed controlsystem according to the third aspect, the first motor driver (201; 211)of each of the plurality of motor drive chains (71; 72) interruptscommunication with the central monitoring means (10) when an abnormalcondition occurred in the motor drive chain (71; 72) to which itbelongs.

According to the rotational speed control system of the fourth aspect ofthis invention, the central monitoring means can intensively monitor thestate of operation of one motor drive chain without being hampered by anabnormal condition that occurred in the other motor drive chain.

In a fifth aspect of this invention, in the rotational speed controlsystem according to the fourth aspect, the first motor driver (201; 211)includes: a communication/control circuit (83) driving the motor (M₁₁;M₂₁) corresponding to itself based on the rotational speed instructingsignal and capable of communicating with the central monitoring means(10); a connector (84) connected to the central monitoring means; andswitches (85) interposed between the connector and thecommunication/control circuit, and the switches are interrupted in themotor drive chain in which an abnormal condition occurred.

According to the rotational speed control system of the fifth aspect ofthis invention, the communication in the fourth aspect can beinterrupted.

In a sixth aspect of this invention, in the rotational speed controlsystem according to the fifth aspect, the second motor driver (202 to206; 212) includes a communication/control circuit (83) capable ofcommunicating with the communication/control circuit (83) of the firstmotor driver (201; 211) in a digital value via the in-chain wiring (51;52), and driving the motor (M₁₂ to M₁₆; M₂₂) corresponding to itselfbased on the rotational speed instructing signal (91; 92).

According to the rotational speed control system of the sixth aspect ofthis invention, the rotational speed instructing signal is supplied fromthe first motor driver to the second motor driver via the in-chainwiring.

In a seventh aspect of this invention, in the rotational speed controlsystem according to the first aspect, in the motor drive chain (71), thesecond motor driver (202 to 206) includes a plurality of second motordrivers, each of which is set with a unique identification code, and theidentification codes and the rotational speed instructing signal aretransmitted from the first motor driver (201) to the second motordrivers (202 to 206).

In an eighth aspect of this invention, in the rotational speed controlsystem according to the seventh aspect, the identification codes and therotational speed instructing signal are transmitted from the secondmotor drivers (202 to 206) to the first motor driver (201) in the motordrive chain (71).

According to the rotational speed control systems of the seventh andeighth aspects of this invention, whether the information transmittedfrom the first motor driver was correctly transmitted to the secondmotor drivers can be confirmed, which in turn allows the transmissionagain from the first driver to the second drivers when the informationwas not correctly transmitted due to contamination with noise or thelike.

In a ninth aspect of this invention, in the rotational speed controlsystem according to the seventh aspect, a code corresponding to afailure that occurred in the second motor driver (201 to 206) istransmitted from the second motor driver to the first motor driver(201).

According to the rotational speed control system of the ninth aspect ofthis invention, the central monitoring means is allowed to recognizewhat kind of failure has occurred in which slave driver.

In a tenth aspect of this invention, in the rotational speed controlsystem according to the first aspect, in the motor drive chain (71), thesecond motor driver (202 to 206) is divided into a plurality ofsub-motor drive chains (71 a, 71 b), and each of the sub-motor drivechains is set with a unique identification code, and the identificationcodes and the rotational speed instructing signal are transmitted fromthe first motor driver (201) to the sub-motor drive chains.

According to the rotational speed control system of the tenth of thisinvention, the sub-motor drive chains can be controlled by differentrotational speeds from one another.

In an eleventh aspect of this invention, a rotational driving systemcomprises: the rotational speed control system recited in any one offirst to tenth aspects; and motors (M₁₁ to M₁₆; M₂₁, M₂₂) in accordancewith the same specifications that are provided correspondingly torespective ones of the motor drivers and the rotational speeds thereofare controlled by the motor drivers corresponding to themselves.

According to the rotational driving system of the eleventh aspect ofthis invention, rotational driving can be supplied to loads on themotors at an equal rotational speed when the loads are equal to eachother.

In a twelfth aspect of this invention, an air blow system comprises: therotational driving system recited in the eleventh aspect, and aplurality of fans (F₁₁ to F₁₆; F₂₁, F₂₂) in accordance with the samespecifications that are provided correspondingly to respective ones ofthe motors (M_(11 to M) ₁₆; M₂₁, M₂₂) and rotationally driven by themotors corresponding to themselves.

According to the air blow system of the twelfth aspect of thisinvention, an equal quantity of air can be blown into a plurality oflocations having intake conductance and exhaust conductance equal toeach other.

In a thirteenth aspect of this invention, a clean bench (CB) comprisesthe air blow system according to the twelfth aspect.

According to the clean bench of the thirteenth aspect of this invention,the same quantity of air is allowed to be blown into a plurality oflocations, thereby suppressing flotation of dust.

In a fourteenth aspect of this invention, an outdoor unit (300) of anair conditioner comprises the air blow system according to the twelfthaspect.

According to the outdoor unit of the air conditioner of the fourteenthaspect of this invention, exhaust balance is improved and efficiency ofthe outdoor unit is enhanced.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

Publications regarding this invention include Japanese PatentApplication Laid-Open Nos. 8-42885 (1996), 11-94418 (1999), and2002-54830.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are block diagrams showing the configurations of an airblow system according to the present embodiment;

FIG. 3 is a schematic diagram showing the structure of a clean bench CBaccording to this invention;

FIG. 4 is a schematic diagram showing the configuration of an outdoorunit 300 of an air conditioner according to this invention; and

FIG. 5 is a block diagram showing the configuration of a conventionalair blow system.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing the configuration of an air blowsystem according to the present embodiment. The air blow system includesa plurality of air blow chains 71 and 72, and a central monitoringdevice 10 intensively monitoring the operations of these chains that areconnected to one another. The air blow chains 71 and 72 are connected toeach other in parallel with respect to the central monitoring device 10via a central monitoring line 4. The central monitoring line 4 has thefunction of transmitting the state of communication and the state ofcontrol of the air blow chains 71 and 72 to the central monitoringdevice 10. While FIG. 1 illustrates the case where the air blow chainsinclude two chains, three or more chains may be connected in parallel.

The air blow chain 71 includes a remote controller 31, and a pluralityof motor drivers 201 and 202. We can understand the motor drivers 201and 202 as a motor driver chain. The motor drivers 201 and 202 areconnected to each other in parallel in a way described later in detail.Motors M₁₁ and M₁₂ are connected correspondingly to the motor drivers201 and 202, respectively. Fans F₁₁ and F₁₂ are attached to the motorsM₁₁ and M₁₂, respectively, and rotated. While FIG. 1 illustrates thecase where two motor drivers are connected in parallel, three or moremotor drivers (accordingly, motors and fans) may be connected inparallel. The fans F₁₁ and F₁₂, the motors M₁₁ and M₁₂, and the motordrivers 201 and 202 are respectively designed in accordance with thesame specifications.

In the air blow chain 71, the remote controller 31 which is a controlcircuit and the central monitoring device 10 are directly connected onlyto the motor driver 201. In this invention, a motor driver to which thecentral monitoring device 10 is directly connected is called a masterdriver, and all other motor drivers are called slave drivers. One masterdriver is set for each air blow chain. The motor driver 201 is themaster driver in the air blow chain 71. The motor driver 202 and all theother motor drivers connected in parallel, if there are, are the slavedrivers in the air blow chain 71.

The air blow chain 72 is configured in the same way as the air blowchain 71. The air blow chain 72 includes a remote controller 32, andmotor drivers 211 and 212 which correspond to the remote controller 31,and the motor drivers 201 and 202 in the air blow chain 71,respectively. We can understand the motor drivers 211 and 212 as a motordriver chain. Motors M₂₁ and M₂₂ are connected correspondingly to themotor drivers 211 and 212, respectively. Fans F₂₁ and F₂₂ are attachedto the motors M₂₁ and M₂₂, respectively, and rotated. While FIG. 1illustrates the case where two motor drivers are connected in parallel,three or more motor drivers (accordingly, motors and fans) may beconnected in parallel. The number of motor drivers connected in parallelmay differ between the air blow chains 71 and 72.

The fans F₂₁ and F₂₂, the motors M₂₁ and M₂₂, and the motor drivers 211and 212 are respectively designed in accordance with the samespecifications. Those specifications may be different between the airblow chains 71 and 72. For the sake of simplicity, the followingexplanation is based on the assumption that the motor drivers 211 and212 have the same configurations as those of the motor drivers 201 and202.

In the air blow chain 72, the remote controller 32 which is a controlcircuit and the central monitoring device 10 are connected only to themotor driver 211. The motor driver 211 is the master driver in the airblow chain 72. The motor driver 212 and all the other motor driversconnected in parallel, if there are, are the slave drivers in the airblow chain 72.

We can understand the central monitoring device 10, the motors M₁₁ andM₁₂, the motor drivers 201 and 202, and the remote controller 31 as arotational driving system supplying rotational driving to the fans F₁₁and F₁₂. We can understand the rotational driving system combined withthe fans F₁₁ and F₁₂ as an air blow system. Or again, we can understandthe rotational driving system further including the motors M₂₁ and M₂₂,the motor drivers 211 and 212, and the remote controller 32 as arotational driving system supplying rotational driving to the fans F₁₁,F₁₂, F₂₁ and F₂₂. We can understand the rotational driving systemcombined with the fans F₁₁, F₁₂, F₂₁ and F₂₂ as an air blow system.

Further, we can understand the central monitoring device 10, the motordrivers 201 and 202, and the remote controller 31 as a rotational speedcontrol system controlling the rotational speeds of the motors M₁₁ andM₁₂. Or again, we can understand the rotational speed control systemfurther including the motor drivers 211 and 212, and the remotecontroller 32 as a rotational speed control system controlling therotational speeds of the motors M₁₁, M₁₂, M₂₁ and M₂₂.

The motor drivers 201, 202, 211 and 212 each include a receiving buffer81 and a transmitting buffer 82. The receiving buffer 81 performs thefunction of receiving information from the central monitoring device 10and the other motor driver (for example, the motor driver 202 for themotor driver 201; the motor driver 212 for the motor driver 211) in theair blow chain to which it belongs. The transmitting buffer 82 performsthe function of transmitting information to the central monitoringdevice 10 and the other motor driver.

The motor drivers 201, 202, 211 and 212 each further include acommunication/control circuit 83. In the motor drivers 201 and 211, thecommunication/control circuits 83 are each connected to the receivingbuffer 81 and the transmitting buffer 82 inside the motor drivers 201and 211, and to the remote controllers 31 and 32 from the outside of themotor drivers 201 and 211, respectively. In the motor drivers 202 and212, the communication/control circuits 83 are each connected to thereceiving buffer 81 and the transmitting buffer 82 inside the motordrivers 202 and 212, and have no connection to the remote controllers 31and 32.

The remote controllers 31 and 32 respectively output rotational speedinstructing signals 91 and 92 setting a motor rotational speed in adigital value or an analog value. The communication/control circuits 83in the motor drivers 201 and 211 which are the master drivers receivethe rotational speed instructing signals 91 and 92 from the remotecontrollers 31 and 32, respectively, drive the motors M₁₁ and M₂₁corresponding to themselves based on those signals, and in turn rotatethe fans F₁₁, and F₂₁. The air blow chains 71 and 72 can adoptrotational speeds different from each other, and in that case, therotational speed instructing signals 91 and 92 take on values differentfrom each other. In this case, the motors can be driven at an equalrotational speed in units of air blow chains. The air blow chains 71 and72 can naturally adopt a rotational speed equal to each other byequalizing the values of the rotational speed instructing signals 91 and92.

The motor drivers 201, 202, 211 and 212 further include first connectors84 and second connectors 86. In each of the motor drivers, both of thefirst connector 84 and the second connector 86 connect the receivingbuffer 81 and the transmitting buffer 82 in parallel between themselvesand the communication/control circuit 83. Switches 85 are furtherprovided between the first connector 84, and the receiving buffer 81 andthe transmitting buffer 82, which are conducting under normal conditionsbut are interrupted by the communication/control circuit 83 underabnormal conditions.

The respective second connectors 86 in the motor drivers 201 and 202 areconnected in parallel with respect to an in-chain wiring 51. Undernormal conditions, the central monitoring device 10 communicates withthe communication/control circuit 83 via the central monitoring line 4and the first connector 84, the receiving buffer 81 in the motor driver201. Accordingly, under normal conditions, information about the stateof operation of the motor driver 202 is supplied to the centralmonitoring device 10 via the second connector 86 in the motor driver202, the in-chain wiring 51, the second connector 86 in the motor driver201, the switches 85 in the motor driver 201, the first connector 84 inthe motor driver 201, and the central monitoring line 4.

The central monitoring device 10 includes a receiving buffer 11, atransmitting buffer 12, and a monitor processing circuit 13. The monitorprocessing circuit 13 receives information from the central monitoringline 4 via the receiving buffer 11, and supplies information to thecentral monitoring line 4 via the transmitting buffer 12.

Likewise, the respective second connectors 86 in the motor drivers 211and 212 are connected in parallel with respect to an in-chain wiring 52.Accordingly, under normal conditions, information about the state ofoperation of the motor driver 212 is supplied to the central monitoringdevice 10 via the second connector 86 in the motor driver 212, thein-chain wiring 52, the second connector 86 in the motor driver 211, thefirst connector 84 in the motor driver 211, and the central monitoringline 4.

As described above, the central monitoring device 10 can intensivelymonitor the operations of the air blow chains 71 and 72. Especially, thestate of operation of each of the motor drivers 201, 202, 211 and 212can be intensively monitored by setting the motor drivers 201, 202, 211and 212 with unique identification codes, and allowing the centralmonitoring device 10 to recognize the identification codes.

Conversely, the rotational speed instructing signal 91 is supplied indigital value mode from the communication/control circuit 83 in themotor driver 201 to the communication/control circuit 83 in the motordriver 202 via the transmitting buffer 82 in the motor driver 201, thesecond connector 86 in the motor driver 201, the in-chain wiring 51, thesecond connector 86 in the motor driver 202, and the receiving buffer 81in the motor driver 202. In this fashion, the respectivecommunication/control circuits 83 in the motor drivers 201 and 202 arecapable of communicating with each other in a digital value, so that themotor driver 202 which is the slave driver can drive the motor M₁₂ andin turn rotate the fan F₁₂ at a rotational speed equal to that fordriving the motor M₁₁ by the motor driver 201 which is the masterdriver.

Likewise, the rotational speed instructing signal 92 is transmitted fromthe motor driver 211 to the motor driver 212. Accordingly, the motordriver 212 which is the slave driver can drive the motor M₂₂ and in turnrotate the fan F₂₂ at a rotational speed equal to that for driving themotor M₂₁ by the motor driver 211 which is the master driver.

Because the motor rotational speeds set by the rotational speedinstructing signals 91 and 92 are transmitted in a digital value betweenthe motor drivers, a plurality of motors can be driven at the samerotational speed in units of air blow chains without depending on thenumber of motor drivers and without depending on the characteristics ofeach motor driver. The rotational speed instructing signals 91 and 92may be a digital value indicative of the value itself of the number ofrotations, or may be a code corresponding to the number of rotations.Alternatively, the signals may indicate the threshold values of theupper limit and lower limit of the number of rotations. In that case,the communication/control circuits 83 included in the master drivers 201and 211 control the numbers of rotations to fall within the rangebetween the two threshold values.

Besides, the central monitoring device 10 can monitor the state ofoperations of the air blow chains 71 and 72 via the central monitoringline 4. With the central monitoring line 4 being connected to thein-chain wirings 51 and 52 via the respective first connectors 84 andsecond connectors 86 in the motor drivers 201 and 211, the centralmonitoring device 10 can intensively monitor the state of operations ofall of the motor drivers 201, 202, 211 and 212.

For example, it is assumed that an abnormal condition occurred in thein-chain wiring 51 of the air blow chain 71. If left unaddressed, theabnormal condition is likely to affect the air blow chain 72 adverselyvia the central monitoring line 4. Upon detection of this abnormalcondition, the motor drivers turn off the switches 85 in all series,conduct communication tests within series of its own, and leave theswitches 85 in the OFF state when an abnormal condition is detected. Theswitches 85 are turned on again only when it is judged that the seriesof its own is under normal conditions, thereby restarting communication.At this time, each of the motor drivers maintains the number ofrotations before the occurrence of the abnormal condition. This isbecause the location of the abnormal condition cannot be identified ifall series remain connected. In order to avoid such adverse effect, thecommunication/control circuit 83 in the motor driver 201 detects theabnormal condition in the in-chain wiring 51 and turns off the switches85 in the motor driver 201. Consequently, the central monitoring device10 can intensively monitor the air blow chain 72, namely the state ofoperations of the motor drivers 211 and 212 without being hampered bythe abnormal condition that occurred in the air blow chain 71.

Conversely, when an abnormal condition occurred in the air blow chain72, the communication/control circuit 83 in the motor driver 211 detectsthe abnormal condition and turns off the switches 85 in the motor driver211. Consequently, the central monitoring device 10 can intensivelymonitor the air blow chain 71, namely the state of operations of themotor drivers 201 and 202 without being hampered by the abnormalcondition that occurred in the air blow chain 71.

Because only the motor drivers 201 and 211 are connected to the centralmonitoring line 4 in the air blow chains 71 and 72, respectively, theswitches 85 and the first connector 84 are not essential constituentrequirements for the motor drivers 202 and 212. However, there is theadvantage of facilitating mass production by designing the motor drivers201 and 202, and the motor drivers 211 and 212 in accordance with thesame specifications, respectively.

The motors M₁₁, M₁₂, M₂₁ and M₂₂ may be provided with rotational speeddetectors P₁₁, P₁₂, P₂₁ and P₂₂, respectively, to detect rotationalspeeds T₁₁, T₁₂, T₂₁ and T₂₂ of the motors M₁₁, M₁₂, M₂₁ and M₂₂. Therotational speeds T₁₁, T₁₂, T₂₁ and T₂₂ are supplied to thecommunication/control circuits 83 in the motor drivers 201, 202, 211 and212, respectively, to contribute to constant-speed driving control.

The rotational driving system including the rotational speed controlsystem and the motors M₁₁, and M₁₂ (or additionally M₂₁ and M₂₂) asdescribed above can supply rotational driving to the fans F₁₁ and F₁₂(or additionally F₂₁ and F₂₂) at an equal rotational speed when the fansF₁₁ and F₁₂ (or additionally F₂₁ and F₂₂) which are loads on the motorsM₁₁ and M₁₂ (or additionally M₂₁ and M₂₂) are equal to each other.

Moreover, the air blow system including the rotational driving systemand the fans F₁₁ and F₁₂ (or additionally F₂₁ and F₂₂) as describedabove can blow an equal quantity of air into a plurality of locationshaving intake conductance and exhaust conductance equal to each other.

In one air blow chain, when a rotational speed instructing signal istransmitted from the master driver to the slave driver, theidentification code of the transmission target may also be transmittedwith the signal. Then, the identification code of its own and therotational speed instructing signal that was transmitted may be returnedfrom the slave driver set with the transmitted identification code tothe master driver. This confirms whether the information transmittedfrom the master driver was correctly transmitted to the slave driver,and in turn allows the transmission again from the master driver to theslave driver when the information was not correctly transmitted due tocontamination with noise or the like.

In the event of a failure in the slave driver, an error code indicativeof the failure may be transmitted from the slave driver to the masterdriver. By transmitting the error code from the master driver to thecentral monitoring device 10, the central monitoring device 10 canrecognize what kind of failure has occurred in which air blow chain anddisplay the kind of failure in the monitor processing circuit 13.

Furthermore, the error code may be transmitted from the slave driver tothe master driver together with the identification code of the slavedriver in which the failure corresponding to the error code occurred. Bytransmitting the error code and the identification code of the slavedriver from the master driver to the central monitoring device 10, themonitor processing circuit 13 can display what kind of failure hasoccurred in which slave driver.

The number of slave drivers may be recognized by calling theidentification codes of the slave drivers in order. The mutualcommunication between the master driver and the slave drivers offersenhanced reliability.

FIG. 2 is a block diagram showing another configuration of the air blowsystem according to this embodiment. The air blow chain 71 includesmotor drivers 202 to 206 which are the slave drivers in addition to themotor driver 201 which is the master driver. As with the motor driver201, the motor drivers 202 to 206 include the receiving buffer 81, thetransmitting buffer 82, the communication/control circuit 83, the firstconnector 84 and the second connector 86, and the switches 85. The motordrivers 202 to 206 drive motors M₁₂ to M₁₆, respectively. Fans F₁₂ toF₁₆ are attached to the motors M₁₂ to M₁₆, respectively, and rotated.

We can understand the central monitoring device 10, the motors M₁₁ toM₁₆, the motor drivers 201 to 206, and the remote controller 31 as arotational driving system supplying rotational driving to the fans F₁₁to F₁₆. We can understand the rotational driving system combined withthe fans F₁₁ to M₁₆ as an air blow system. We can understand the motordrivers 201 to 206 as a motor driver system. Moreover, we can understandthe central monitoring device 10, the motor drivers 201 to 206, and theremote controller 31 as a rotational speed control system controllingthe rotational speeds of the motors M₁₁ to M₁₆.

The slave drivers, the motors driven by the slave drivers and the fansattached to the motors in the air blow chain 71 have sub-air blow chains71 a and 71 b. In FIG. 2, the sub-air blow chain 71 a includes the motordrivers 202 and 203, the motors M₁₂ and M₁₃, and the fans F₁₂ and F₁₃,and the sub-air blow chain 71 b includes the motor drivers 204 to 206,the motors M₁₄ to M₁₆, and the fans F₁₄ to F₁₆. We can understand themotor drivers 202 and 203, and the motor drivers 204 to 206,respectively, as separate sub-motor driver systems.

A unique identification code may be supplied to each sub-air blow chain.In one air blow chain, when a rotational speed instructing signal istransmitted from the master driver to the slave drivers in units ofsub-air blow chains, the identification code indicative of the sub-airblow chain may also be transmitted with the signal. The sub-air blowchains can be controlled by different rotational speeds from oneanother.

FIG. 3 schematically illustrates a structure of a clean bench CB as anapplicable example of this invention.

In the clean bench CB, a semiconductor wafer W is subjected to cleaningand drying processes. Specifically, the semiconductor wafer W istransferred in the direction of the arrow in the drawing by transfermeans CV which adopts a conveyor, for example, and is subjected to acleaning process, and then a drying process.

At this time, in order for the above processes to be performed in anenvironment with a small amount of dust, clean air G₁ and G₂ aresupplied to respective positions for the cleaning process and the dryingprocess in the clean bench CB. The clean air G₁ is introduced into theclean bench CB by a fan F₁ which takes in the outside air H and exhaustsit via a filter K₁, and the clean air G₂ is introduced into the cleanbench CB by a fan F₂ which takes in the outside air H and exhausts itvia a filter K₂. The drawing schematically illustrates less dust in theclean air G₁ and G₂ than in the outside air H by the number of dots inthe respective arrows.

When the clean air G₁ and G₂ are introduced into the same clean bench CBfrom a plurality of locations as described above, it is desirable thatthose quantities of air be set to be the same, so that flotation of dustis avoided that can come from unbalanced air flow. Because the fansF_(1 and F) ₂ are usually designed in accordance with the samespecifications, it is desirable that the rotational speeds of the fansbe the same.

To this end, the fans F₁₁ and F₁₂ (or the fans F₂₁ and F₂₂) shown inFIG. 1 may be adopted as the fans F₁ and F₂ to thereby set thequantities of air to be the same. This allows the same quantity of airto be blown into a plurality of locations, thereby suppressing flotationof dust.

The air blow system is applicable not just to the clean bench CB. FIG. 4schematically illustrates the configuration of an outdoor unit 300 of anair conditioner according to this invention. The outdoor unit 300includes motors M₁ and M₂, and the fans F₁ and F₂ rotated by the motors,respectively. The motors M₁₁ and M₁₂ (or M₂₁ and M₂₂), and the fans F₁₁and F₁₂ (or the fans F₂₁ and F₂₂) shown in FIG. 1 may be adopted as themotors M₁ and M₂, and the fans F₁ and F₂, respectively. The outdoor unit300 can improve exhaust balance and enhance its efficiency.

The sub-air blow chains as shown in FIG. 2 may be included in the airblow systems adopted in the clean bench CB and the outdoor unit 300 asdescribed above. For example, they may be adopted to different cleanbenches and outdoor units 300 in units of sub-air blow chains.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A rotational speed control system, comprising: (a) at least one ormore motor drive chains (71; 72) each comprising: (a-1) rotational speedinstructing means (31; 32) outputting a rotational speed instructingsignal (91; 92) setting a motor rotational speed; (a-2) a first motordriver (201; 211) receiving said rotational speed instructing signalfrom said rotational speed instructing means and driving a motor (M₁₁;M₂₁) corresponding to itself based on said rotational speed instructingsignal; and (a-3) at least one second motor driver (202 to 206; 212)capable of communicating with said first motor driver in a digitalvalue, receiving said rotational speed instructing signal from saidfirst motor driver and driving a motor (M₁₂ to M₁₆; M₂₂) correspondingto itself based on said rotational speed instructing signal, and (b)central monitoring means (10) monitoring the operations of said firstand second motor drivers in units of said motor drive chains bycommunicating with said first motor driver of each of said motor drivechains.
 2. The rotational speed control system according to claim 1,wherein in each of said motor drive chains (71; 72), (a-4) an in-chainwiring (51; 52) connecting said first motor driver (201; 211) and saidsecond motor driver (202; 212) to each other is further provided.
 3. Therotational speed control system according to claim 1, wherein said motordrive chains (71; 72) include a plurality of motor drive chains.
 4. Therotational speed control system according to claim 3, wherein said firstmotor driver (201; 211) of each of said plurality of motor drive chains(71; 72) interrupts communication with said central monitoring means(10) when an abnormal condition occurred in the motor drive chain (71;72) to which it belongs.
 5. The rotational speed control systemaccording to claim 4, wherein said first motor driver (201; 211)includes: a communication/control circuit (83) driving said motor (M₁₁;M₂₁) corresponding to itself based on said rotational speed instructingsignal and capable of communicating with said central monitoring means(10); a connector (84) connected to said central monitoring means; andswitches (85) interposed between said connector and saidcommunication/control circuit, and said switches are interrupted in saidmotor drive chain in which an abnormal condition occurred.
 6. Therotational speed control system according to claim 5, wherein saidsecond motor driver (202 to 206; 212) includes a communication/controlcircuit (83) capable of communicating with said communication/controlcircuit (83) of said first motor driver (201; 211) in a digital valuevia said in-chain wiring (51; 52), and driving said motor (M₁₂ to M₁₆;M₂₂) corresponding to itself based on said rotational speed instructingsignal (91; 92).
 7. The rotational speed control system according toclaim 1, wherein in said motor drive chain (71), said second motordriver (202 to 206) includes a plurality of second motor drivers, eachof which being set with a unique identification code, and saididentification codes and said rotational speed instructing signal aretransmitted from said first motor driver (201) to said second motordrivers (202 to 206).
 8. The rotational speed control system accordingto claim 7, wherein said identification codes and said rotational speedinstructing signal are transmitted from said second motor drivers (202to 206) to said first motor driver (201) in said motor drive chain (71).9. The rotational speed control system according to claim 7, wherein acode corresponding to a failure that occurred in said second motordriver (201 to 206) is transmitted from said second motor driver to saidfirst motor driver (201).
 10. The rotational speed control systemaccording to claim 1, wherein in said motor drive chain (71), saidsecond motor driver (202 to 206) is divided into a plurality ofsub-motor drive chains (71 a, 71 b), and each of said sub-motor drivechains is set with a unique identification code, and said identificationcodes and said rotational speed instructing signal are transmitted fromsaid first motor driver (201) to said sub-motor drive chains.
 11. Arotational driving system, comprising: the rotational speed controlsystem recited in any one of claims 1 to 10; and motors (M₁₁ to M₁₆;M₂₁, M₂₂) in accordance with the same specifications that are providedcorrespondingly to respective ones of said motor drivers and therotational speeds thereof are controlled by said motor driverscorresponding to themselves.
 12. An air blow system, comprising: therotational driving system recited in claim 11, and a plurality of fans(F₁₁ to F₁₆; F₂₁, F₂₂) in accordance with the same specifications thatare provided correspondingly to respective ones of said motors (M₁₁ toM₁₆; M₂₁, M₂₂) and rotationally driven by said motors corresponding tothemselves.
 13. A clean bench (CB) comprising the air blow systemrecited in claim
 12. 14. An outdoor unit (300) of an air conditionercomprising the air blow system recited in claim 12.